The present system concerns a device and method for introducing a machining electrode, especially a wire or bar sinking electrode to an electrode guide system oan electrical discharge machining (EDM) machine.
EDM machines are used to machine work pieces by electric spark discharge between an electrically conducting work piece and a machining electrode. In particular, the work piece can be cut by means of a wire electrode or machine with a bar sinking electrode by boring or cavity sinking. In this case, in addition to ablation of the material particles of the work piece, the machining electrode itself is also ablated. As a result, new electrode material must continuously be supplied. For example, a wire electrode is unwound from a spool or a bar-like machining electrode and is guided through the work zone of the EDM machine in order to continuously supply new electrode material.
A new machining electrode must initially be prepared for feed and, in particular, brought to a position suitable for feed (hereafter referred to as xe2x80x9cintroduction of the machining electrodexe2x80x9d). Corresponding preparation or introduction devices are described in EP 0 161 657 (xe2x80x9cDevice for guiding a wire or band-like cutting electrode on a machine toolxe2x80x9d) and in JP 5-185322 (xe2x80x9cElectrical wire EDM machinexe2x80x9d). In both cases, preparation is by hand.
There is a need to provide an improved device and an improved method for preparing a machining electrode, especially a wire electrode or bar sinking electrode of an EDM machine for feed into an electrode guide system.
The above need is met by the present system by using a device for introducing a machining electrode, especially a wire electrode or a bar sinking electrode to an electrode guide system of an EDM machine having at least one means of suction and advance to draw in and advance the machining electrode and at least one pressure equalization device to reduce a fluid pressure provided in front of the suction and advance device in the direction of electrode advance.
The above need is also met by the present system by using an electrode change device, which comprises at least two devices according to the teachings of the present system for preparation of the machining electrode, and is movable relative to an input element of the electrode guide system for alternating introduction of the corresponding machining electrode.
Further, the above need is a met by a method for introduction or preparation of a machining electrode (e.g, a wire electrode or a bar sinking electrode) to an electrode guide system of an EDM machine, in which a fluid is first injected between a main nozzle formed as outer nozzle and an inner nozzle. Next, an underpressure is produced by this fluid injection in a hole of the inner nozzle and a machining electrode is drawn in and the drawn-in machining electrode is advanced. The fluid pressure is then reduced in at least one pressure equalization device connected in front of the main nozzle.
Unlike the known devices and methods for preparing a machining electrode, the machining electrode of the present system can also be drawn in during threading into the preparation device. This is particularly advantageous for fine erosion wires (electrodes) that can scarcely be manipulated by hand without aid. Because of this, the area of application of EDM machines for novel uses is expanded and, the work demands for an operator are substantially reduced. Moreover, the pressure built up in the device at the entry of the device for drawing-in and advance of the machining electrode can be at least largely reduced by the pressure equalization or pressure relief device and undesired emergence of pressure-generating fluid thereby avoided at the input of the device.
According to a variant of the present system, the suction and advance device includes a main nozzle that is essentially aligned along a main axis. A fluid can be injected into the main nozzle. By injection of fluid into the main nozzle on its injection side, an underpressure that initially draws in the machining electrode can be generated and the drawn-in machining electrode then advanced. In this manner the suction and advance devices are implemented in particularly simple fashion. It is also possible to transport the machining electrode with the fluid used for the suction process through the electrode guide system of the EDM machine.
According to another variant, the main nozzle is an outer nozzle with an inner nozzle and a tapering flow gap running between the outer and inner nozzle. The fluid can be injected into a flow gap between the inner wall of the main nozzle and the outer wall of the inner nozzle. The machining electrode can initially be drawn in through the hole of the inner nozzle and then advanced.
The underpressure required for the suction process can therefore be generated particularly simply and effectively.
According to yet another variant, at least one relief chamber is arranged along the main axis in front of the entry to the hole facing away from the main nozzle as a pressure equalization device. The fluid flowing to the input of the device from this relief chamber can be taken off through a bypass after it has reduced its overpressure in the relief chamber. Relief chambers are particularly suited for pressure equalization. The fluid, if it escapes into the chamber, is dammed up there and loses flow energy, especially when the chamber is also preferably filled with fluid. The fluid is discharged from the device through the bypass of the relief chambers according to the pressure prevailing there. In this manner, the situation is avoided in which the fluid emerges in an undesired and uncontrolled fashion, for example, at the output of the device according to the invention.
In another variant the device includes two or more relief chambers. In principle, it is sufficient to use only one relief chamber. To largely avoid undesired fluid escape at the most tolerable possible cost, however, it is expedient to use two or more relief chambers arranged in sequence, which cause a cascade-like pressure reduction.
Fluid is also preferably dischargeable from the relief chambers through the bypasses essentially against gravity. In principle, it is possible to divert the fluid in any direction. This preferably occurs against gravity, but a situation occurs in which diversion only takes place if an overpressure develops in the chamber. That is, during advance of the machining electrode in the electrode guide system of the EDM machine, fluid will penetrate into the relief chamber owing to the counterpressure prevailing in the system. Since this occurs under a certain pressure or counterpressure, part of the fluid will traverse the relief chamber in a jet along the machining electrode. Another part, however, remains in the relief chamber so that this is filled with fluid. As soon as the relief chamber is filled with fluid, the fluid along the machining electrode is braked by the other fluid at rest, diverted and possibly swirled so that the fluid pressure in and behind the relief chamber is significantly reduced. As a result, the fluid pressure in the relief chamber will build up to an overpressure and convey fluid from the bypass against gravity.
In principle, discharge of fluid from the relief chambers could also be achieved with a bypass with gravity if this were to have a sufficiently narrow diameter, for example. However, the discharge of fluid from the relief chambers is achieved more simply and more effectively in the manner described above.
The separation devices make it possible, for example, to cut a wire-like machining electrode after preparation in the device. Since the machining electrode is generally fed from an endless roll, the cutting device is also required in order to be able to separate the machining electrode at the end of the unwinding process from a partial piece remaining on the roll or in any case outside of the electrode guide system without involvement of an operator.